1. Field of the Invention
The present invention relates generally to a manganese dry battery which does not contain such heavy metals as mercury and cadmium, and therefore are free from environmental pollution caused by these heavy metals. In particular, the present invention is concerned with an improvement of the composition of alloy for an anode can of such dry battery.
2. Description of the Prior Art
Heretofore, zinc alloys containing 0.03-0.1 wt. % of cadmium and 0.1-0.3 wt. % of lead have generally been employed for configuring a zinc can which also serves as an anode of the manganese dry battery, in order to enhance its workability and mechanical strength which are necessary in the manufacturing process of zinc cans and to suppress possible corrosion of the anode zinc can during storing of the dry battery configured with the anode zinc can.
Environmental pollution due to the heavy metals remaining in waste dry batteries has recently become a serious social concern. At present, the dry batteries are therefore being produced without adding cadmium out of these heavy metals to the zinc alloy for the anode can. However, in view of enhancing the workability and mechanical strength of the anode zinc can and preventing the corrosion of the anode zinc can, which is a cause for the self-discharge of the dry battery configured with the anode zinc can, the content of lead in the zinc alloy is increased to, for instance, 0.3-0.8 wt. % in general.
Lead is however attracting attention in this art as another serious cause for the environmental pollution, similar to mercury and cadmium. Reduction of the amount of lead to be added to the alloy composition, or production of the dry battery without adding any lead is therefore of urgent necessity.
However, as already well known, the proposed reduction or complete exclusion of lead from the zinc alloy, greatly deteriorates the workability and the mechanical strength of the alloy and invites corrosion of the zinc alloy with the decrease in the lead content.
Of these unsolved problems, as a means for solving the corrosion of the zinc alloy, it is already known to use a zinc alloy added with manganese, indium or bismuth as the anode powder for configuring an alkaline-manganese dry battery.
However, when an alloy is produced by adding these metals, the workability of the alloy tends to decrease with the decrease in the added amount of lead, as compared with an anode can made of the prior art zinc alloy added solely with lead.